Subtract $2i$ from $ \dfrac{1}{2} $ to get $ \dfrac{ \color{purple}{ -4i+1 } }{ 2 }$.

Step 1: Write $ 2i $ as a fraction by putting $ \color{red}{ 1 } $ in the denominator.

Step 2: To subtract raitonal expressions, both fractions must have the same denominator.
We can create a common denominator by multiplying the second fraction by $\color{blue}{2}$.

$$ \begin{aligned} \frac{1}{2} -2i & \xlongequal{\text{Step 1}} \frac{1}{2} - \frac{2i}{\color{red}{1}} = \frac{ 1 }{ 2 } - \frac{ 2i \cdot \color{blue}{ 2 }}{ 1 \cdot \color{blue}{ 2 }} = \\[1ex] & \xlongequal{\text{Step 2}} \frac{ \color{purple}{ 1 } }{ 2 } - \frac{ \color{purple}{ 4i } }{ 2 }=\frac{ \color{purple}{ -4i+1 } }{ 2 } \end{aligned} $$